CARBON DIOXIDE EXCHANGE DURING THE SHORT INDUCTION PERIOD 1345 



The observations of Emerson and Lewis (1941) already were discussed 

 in chapter 29. In these experiments, the rates of exchange of both carbon 

 dioxide and oxygen were measured manometrically, by means of two reac- 

 tion vessels of different volume, containing the same amount of liquid. 

 The experiments were carried out at low light intensities (near the com- 

 pensation puint), and high carbon dioxide concentration (5%), thus repeat- 

 ing the experimental conditions of Warburg and Negelein. The results 

 were shown in figure 29. 3B. If the ratio AO2/— ACO2 were unity (for 

 both respiration and photosynthesis), the two curves in the figure would 

 be mirror images. This relation is not reached until 20 or 40 minutes after 

 the beginning of illumination. At first, the picture is dominated by a 



TIME 



Fig. .33.1.3. Diagram showing the pai't of CO2 exchange attributed to some process 

 otlier than respiration and photosynthesis (after Emerson and Lewis 1941). 



"carbon dioxide gush," which reaches its peak in the first minute of illu- 

 mination (when the value of AO2/ ACO2 drops to —0.15). It subsides slowly, 

 perhaps with a secondary wave of carbon dioxide liberation, 5 or 10 minutes 

 later. The oxygen curve is much more regular (the slight maximum of 

 oxygen consumption, coinciding with the carbon dioxide gush, may or may 

 not be real). Assuming — in contrast to Kostychev's suppositions — that 

 the oxygen curve gives the true measure of photosynthesis during the induc- 

 tion period, and postulating that respiration is constant, Emerson and 

 Lewis constructed from figure 29. SB the curve reproduced in figure 33.13, 

 where the shaded areas represent extra liberation of carbon dioxide in light 

 attributable to the gush (and its reversal in the dark). 



The volume of the gush (shaded area, showing the difference between 

 the assumed carbon dioxide exchange and the observed exchange) increases 

 at first with increasing light intensity, but "light saturation" is reached in 



